CAMBRIDGE, Mass.  Singer/songwriter Chan Marshall, who performs under the name Cat Power, was showcasing other writers' songs Sunday, but the performance, which ranged from spellbinding to meandering, was all hers.

Playing solo on a small stage drenched in darkness, Marshall enraptured a reverent audience through the early part of her set but lost momentum  and some of the crowd  during a lengthy and rambling stretch at the piano.

Marshall, an Atlanta native, has been performing her ragged, dreamy songs since the early 1990s. She got her big break in 1996 when she released the album Myra Lee on Sonic Youth drummer Steve Shelley's label, Smells Like Records.

Last week, Marshall released The Covers Record, which includes her renditions of songs by Moby Grape, the Rolling Stones, Bob Dylan and the Velvet Underground. This was the second stop of a 15-city tour.

When she stepped on stage, the small upstairs room at the Middle East Club was so silent that a sip of beer being swallowed was audible, and the click and flare of a lighter was like a bomb blast. Marshall, who is known for being shy, moody and unpredictable during her performances, started strong, with folk-rocker Michael Hurley's haunting "Devil's Daughter" (RealAudio excerpt), which appears on The Covers Record.

Head down, her heavy auburn bangs covering her eyes, Marshall wrapped her long fingers around the neck of her 12-string acoustic guitar and began to play, with no introductions or preliminaries.

Despite this being the second of two sold-out shows in a day, Marshall's slightly nasal voice was strong, controlled and achingly beautiful, full and resonant, and marked by silken overtones. Her sometimes shaky guitar playing was self-assured.

After a couple of songs on guitar, Marshall moved to a piano  rented for her by the club  and played a focused and lovely version of Nina Simone's "Wild Is the Wind" (RealAudio excerpt). She started another song, then stopped to complain briefly about the sound in the small room.

"I hope you can hear this, because I can't. This piano is playing to"  she gestured broadly to the wall behind her  "over there somewhere."

Marshall did not throw a Fiona Apple-style fit, but her focus was lost from that moment on. She started and stopped several songs. Eventually, she seemed to abandon the idea of playing songs and lapsed into random tinkering and practice exercises, punctuated by giggling and throat clearing, all of which prompted some less-tolerant audience members to shake their heads and shuffle out the club's back door.

But for others, Marshall could do no wrong, and even her semi-incoherent piano ramblings were entertaining in their own way. At one point, as Marshall played in the darkness, her hands moving gracefully across the keyboard, she looked as if she had lapsed into a dream state and had taken her audience with her.

Her interlude at the piano took something out of Marshall that she never quite recovered. She strapped on an electric guitar but never really played it. Prompted by flashes from a photographer's camera, Marshall rambled a bit about epileptic seizures caused by flashing lights from police cruisers. She strummed a chord or two, relaxed, and in good humor chatted with the audience a bit more. She said her thanks and left the stage.

Local music promoter Billy Ruane, who attended both shows, was enthusiastic despite Marshall's inconsistent performance. "Isn't she great? The first show was good; she played for over an hour. But this was even better. She played more piano, and she was more relaxed."

Mark Gratiano, a student living in Malden, said, "Her lyrics are so introspective and thoughtful. She's pretty damn odd. I like her."